Borneo’s Rivers: A Paradise Under Threat

Only a small part of Borneo today still has clean, unpolluted water like this. Model: Martha Jalung.

Kalimantan’s rivers, once celebrated as the “Island of a Thousand Rivers”, are rich in biodiversity and vital to Indigenous communities and ecotourism. But mercury pollution from gold mining and deforestation from palm oil threaten these ecosystems and iconic rivers like the Kahayan and Barito.

BORNEOTRAVEL - Tarakan: Borneo’s rivers, the lifeblood of Kalimantan, Indonesia’s portion of the island, are a cornerstone of ecotourism, drawing adventurers and nature lovers to their pristine beauty. 

These waterways, winding through lush rainforests, harbor millions of species, with fish and shrimp forming a vibrant backbone of aquatic biodiversity. 

Rivers like the Kapuas and Mahakam teem with over 300 fish species, including the endemic Puntius and Rasbora, alongside freshwater shrimp vital to local ecosystems and livelihoods. The exotic vistas, emerald canopies reflected in crystal waters, offer a breathtaking backdrop for eco-travelers seeking untouched wilderness.

Yet, this natural splendor is under siege. Major rivers, such as the Barito (900 km) and Kahayan, face severe mercury pollution from artisanal small-scale gold mining (ASGM). Mercury levels in the Kahayan River have reached 2,260 ng/L, more than double Indonesia’s drinking water standard of 1,000 ng/L, endangering aquatic life and human health. 

Large-scale palm oil plantations, covering 618,000 hectares in South Kalimantan alone, exacerbate the crisis through deforestation and chemical runoff, clouding once-clear waters and disrupting habitats for fish and shrimp populations critical to both ecology and local fisheries.

The stakes for ecotourism and biodiversity are immense. Declining fish stocks—down 30% in rivers like the Barito over two decades—threaten the livelihoods of indigenous Dayak communities and the appeal of Kalimantan’s rivers as ecotourism destinations. 

Ancient Hindu-Indian texts dubbed Borneo Varuna-dvipa, or “Island of a Thousand Rivers,” for its vast waterway network, but without urgent action, this legacy risks becoming a memory. Conservation efforts must prioritize protecting these rivers to preserve their ecological and cultural value.

Biodiversity at Risk

The rivers of Kalimantan are ecological powerhouses, supporting a rich tapestry of life. Over 300 fish species, including the vibrant Puntius and Rasbora, thrive in rivers like the Mahakam, alongside freshwater shrimp that sustain both ecosystems and local fishing communities. 

The Mahakam dolphin, a critically endangered species unique to its namesake river, is a symbol of this biodiversity, with fewer than 100 individuals remaining. However, pollution and habitat loss have slashed fish populations by up to 30% in rivers like the Barito over the past two decades, threatening food security for indigenous Dayak communities and diminishing the allure of ecotourism.

Threats from Mining and Plantations

Mercury pollution from ASGM is a primary culprit in the degradation of Kalimantan’s rivers. In Central Kalimantan, the Kahayan River’s mercury levels—2,260 ng/L—pose severe risks to aquatic life and human health, with 43,000 miners contributing to global mercury emissions exceeding 1,000 tons annually. 

Palm oil plantations, spanning 618,000 hectares in South Kalimantan, drive deforestation, with chemical runoff and soil erosion clouding rivers and disrupting shrimp and fish habitats. Recent X posts highlight coal mining waste spills in the Malinau River, while the $20 billion Mentarang Induk Dam in North Kalimantan threatens to flood indigenous lands and fragment river ecosystems.

Conservation Efforts Underway

Conservation groups are mobilizing to save Borneo’s rivers. The World Wide Fund for Nature (WWF), through its Heart of Borneo Initiative launched in 2007 with Indonesia, Malaysia, and Brunei, protects 220,000 km² of rainforest, including vital river catchments. WWF-Indonesia monitors biodiversity in the Hulu Kapuas Landscape, home to 7,500 Bornean orangutans, and supports elephant habitat restoration in Tulin Onsoi. 

The Borneo Orangutan Survival Foundation has reforested 2,000 hectares in East Kalimantan, bolstering river-adjacent ecosystems. Indonesia’s commitment to the Minamata Convention on Mercury (2013) aims to reduce mercury use, but inconsistent enforcement underscores the need for stricter regulations and community-led restoration to secure the “Island of a Thousand Rivers” for future generations.

-- Masri Sareb Putra

References

• Gaveau, D. L. A., et al. (2022). Patterns of infringement, risk, and impact driven by coal mining permits in Indonesia. Ambio, 51(6), 1478–1491. https://doi.org/10.1007/s13280-021-01657-1

• Greenpeace Southeast Asia. (2017). Dirty bankers: How HSBC is financing forest destruction. https://www.greenpeace.org/southeastasia/report/439/Dirty-Bankers/

• Krisnawati, H., & Adinugroho, W. C. (2014). Deforestation in Kalimantan: Spatial and temporal analysis. Center for International Forestry Research (CIFOR). https://www.cifor.org/publications/pdf_files/WPapers/WP-141.pdf

• Mongabay. (2025, March 14). ‘Heart of Borneo’ dams raze Indigenous forests for Indonesia green energy drive. https://news.mongabay.com/2025/03/heart-of-borneo-dams-raze-indigenous-forests-for-indonesia-green-energy-drive/

• Pure Earth. (2013). Mercury hotspots in Indonesia: Artisanal and small-scale gold mining. https://www.pureearth.org/wp-content/uploads/2014/01/Indonesia-Mercury-Report.pdf

• WWF. (n.d.). Freshwater ecosystems. https://wwf.panda.org/discover/our_focus/freshwater/

• WWF. (n.d.). Heart of Borneo (HoB). https://wwf.panda.org/discover/our_focus/forests_practice/heart_of_borneo/

• WWF-Indonesia. (n.d.). Kalimantan: Conservation programs. https://www.wwf.id/en/kalimantan